This invention relates to an apparatus for separating liquids having different densities, such as a hydrocarbon layer floating on a fluid surface.
Many chemical and refining processes use surge vessels which may contain small amounts of an immiscible second liquid phase; e.g., oil and water. If the minor phase is the heavy phase, it can be easily collected and removed separately, or it may be allowed to pass along with the light phase with no special provision needed to avoid accumulation. This is not the case if the minor phase is the light phase. By the very nature of surge vessels, the outlet is at or near the bottom of the vessel. Light phase tends to separate and accumulate in the vessel. Since the liquid level fluctuates during operation (again, the very nature of surge vessels) removal of the upper phase as a separate stream is necessary to avoid slugs of upper phase in the outlet line.
Removal of upper phase presents difficulties. A float can be used to position an outlet pipe to draw off upper phase. However, the moveable parts needed for this type of device are generally considered to be not very reliable for process vessels that operate for several years between turnarounds and floats are usually unacceptable on that basis. The most common method used is to periodically skim the vessel by adjusting liquid level to be in the proper relationship to a skimming nozzle on the side of the vessel. Upper phase is then drawn off through the skimming nozzle. This method is awkward because it requires (1) adjustment of vessel inventory to get the level to the proper position, (2) additional gauge glasses on the vessel to detect the presence and amount of upper phase and (3) the skimming to be done manually.
Mechanical skimmers frequently require maintenance and attention for effective operation, thereby resulting in reduced efficiency in the event of a malfunction.
Applicant is not aware of any prior art which, in his judgment as one skilled in this particular art, would anticipate or render obvious the present invention. However, for the purpose of fully developing the background of the invention, and establishing the state of requisite art, the following art is set forth: U.S. Pat. Nos. 3,752,318; 4,564,449; 3,862,040.